No offense to your brother or sister, but making such trite statements usually shows a weak mind and horrible intellectual disposition. Hopefully when your niece gets into the real world she will have a conversion similar to David Horowitz.
My sister and brother-in-law lean a little to the left as well.
My parents are lifelong Dems (holdover from FDR - Dad is a WWII vet).
I don't have political discussions with my family.